1. Field:
The present disclosure relates generally to engines and, in particular, to a method and apparatus for reducing noise generated during operation of an engine. Still more particularly, the present disclosure relates to a method and apparatus for reducing noise generated by the exhaust jet of an engine.
2. Background:
An aircraft may generate different types of noise during different phases of flight. These different phases of flight may include taxiing, takeoff, landing, cruising, ascending, descending, and/or other phases of flight. In some cases, the noise generated by an aircraft may be undesirable to the passengers and/or crew onboard the aircraft. For example, noise generated during a cruise phase of flight may be undesirable to the passengers and/or crew of an aircraft.
One source of the noise generated during operation of an aircraft may be the operation of an engine of the aircraft. In particular, the flow of exhaust exiting an engine of an aircraft during operation of the engine may contribute to the undesirable noise produced during operation of an aircraft. The flow of exhaust exiting an engine is referred to as an exhaust jet. The exhaust jet is a stream of exhaust gases that flow out of the engine through a nozzle system for the engine. This stream of gases is used to move the aircraft. The pattern with which the exhaust jet flows out of the nozzle system may be referred to as an exhaust plume.
When the exhaust jet exits the nozzle system at supersonic speeds and when the exhaust jet exiting the nozzle has a pressure that is different from the pressure of the ambient air around the exhaust jet, a shock-cell pattern may form in the exhaust jet. This shock-cell pattern may be one factor that contributes to the noise generated during operation of an engine of an aircraft. The noise associated with this shock-cell pattern is referred to as shock-associated broadband noise or shock-cell noise.
A number of different mechanisms have been used to reduce the amount of noise generated during operation of an engine. These mechanisms include adding chevrons and/or serrations to one or more nozzles in the nozzle system for the engine. However, these currently available mechanisms for reducing the noise generated by an engine may not reduce the noise to within selected tolerances. In particular, currently available mechanisms may not reduce the shock-cell noise generated by an engine during a cruise phase of flight to within selected tolerances.
Therefore, it would be desirable to have a method and apparatus that takes into account one or more of the issues discussed above as well as possibly other issues.